Subatomic Par-cles —  Subatomic particles in an atom are Protons, Neutrons, and Electrons. Neutron Electron Proton Protons —  The amount of positive charge varies with each element. —  A proton is a positively charged subatomic particle that is found in the nucleus of an atom. —  Mass of 1 proton = 1.674 x 10-­‐24 g Electrons —  Thomson discovered the electron —  An electron is a negatively charged subatomic particle that is found in the space outside the nucleus. —  Mass of 1 electron = 9.11 x 10-­‐28 g Neutrons —  A neutron is a neutral subatomic particle that is found in the nucleus of an atom. —  Its mass is almost exactly that of a proton. —  1 neutron = 1.675 x 10-­‐24 g Atomic Number —  Atoms of a specific element always have the same number of protons. —  For example, there is only one proton in the nucleus of each and every hydrogen atom. Hydrogen has an atomic number of one. —  The atomic number of an element=The number of protons in an atom of that element. —  The atomic number of an element also equals the number of electrons. 7 N 14.00 Atomic Number Mass Number —  The mass number of an atom is the sum of the protons and neutrons in the nucleus of that atom. —  An atom of aluminum with 13 protons and 14 neutrons has a mass number of 27. —  Remember, the mass number is the larger of the two numbers you see on the Periodic Table. Number of neutrons= Mass number -­‐ Atomic number 7 Atomic Mass N 14.00 Let’s Prac-ce! —  How many electrons are there in the element titanium? (Symbol-­‐ Ti) —  How many protons are there in oxygen? (O) —  What is the atomic number of phosphorus? (P) —  What is the mass number of potassium? (K) —  How many neutrons does neon have? (Ne) —  How many neutrons does chlorine have? (Cl) Isotopes —  Every atom of a given element does NOT have the same number of neutrons. —  Isotopes of atoms of the same element have different numbers of neutrons and mass numbers —  Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons. —  Isotopes of oxygen-­‐ (oxygen-­‐16, oxygen-­‐17, oxygen-­‐18) Isotopes of Hydrogen